This invention relates to a multi-layered thin-film functional device having stacked thin films and magnetoresistance effect element used in a magnetic sensor. In the field of the functional devices such as magnetoresistance effect elements used for magnetic sensors, electronic elements, and so on, there is a powerful stream toward micro-fabrication and high performance. Along with the improvements in vacuum technologies and film-stacking technologies, stacked thin films have come to be often used as functional devices. Conventional technologies of these multi-layered thin-film functional devices are explained below taking a magnetoresistance effect element using a ferromagnetic thin film.
Magnetic resistance effect is the phenomenon that electric resistance changes when a magnetic field is applied to a magnetic body, and it is used in magnetic sensors, magnetic head, or the like. Ferromagnetic thin films of Ni--Fe alloys, for example, are employed in magnetoresistance effect elements (MR elements) for reading external magnetic field signals, utilizing their anisotropic magnetoresistance effects (AMR), i.e., the phenomenon that the electric resistance changes depending upon the positional relation between the current flowing in a magnetic body and the magnetic orientation.
Also remarked recently are magnetoresistance effect films made by alternately stacking ferromagnetic layers and nonmagnetic layers in cycles of several nm to several decades of nm. In these multi-layered thin films, electric resistance changes depending upon whether the magnetic orientations of ferromagnetic layers opposed to each other via a non-magnetic layer are parallel or not. This phenomenon is called giant magnetoresistance (GMR), and researches are under progress toward the application of this nature, similarly to the anisotropic magnetoresistance effect, in magnetoresistance effect elements (GMR elements) for reading external magnetic signals.
Additionally, large hopes are placed on the giant magnetoresistance effect because it promises a larger change in resistance than the anisotropic magnetoresistance effect also when the film is thin. There are different types of film structures exhibiting giant magnetoresistance effects. Among them, a film structure of one type represented by Fe/Cr artificial lattice films (Phys. Rev. Lett. 61(1988)2472) and Co/Cu artificial lattice films (J. mag. mag. mater. 94(1991)L1), for example, has an anti-ferromagnetic coupling type magnetic interaction between ferromagnetic layers, and changes in resistance are obtained in response to an external magnetic field to change relative directions of magnetic moments between the ferromagnetic. In a film structure of another type represented by Co/Cu/NiFe artificial lattice films (J. Phys. Soc. Jpn. 60(1991)2827), two or more different ferromagnetic layers are used in a multi-layered film made up of a ferromagnetic layer and a non-magnetic layer, and a difference in coercive force of these ferromagnetic layers to change relative directions of magnetic moments between the magnetic layers and thereby obtain changes in resistance in response to an external magnetic field.
Also proposed is a spin valve structure (for example, NiFe/Cu/NiFe/FeMn film (J. Appl. Phys. 69(1991)4774)) having a sandwich film stacking a ferromagnetic layer, non-magnetic layer and ferromagnetic layer and having a weak magnetic interaction among the magnetic layers, in which the resistance can be readily switched by providing an anti-ferromagnetic layer in contact with one of the ferromagnetic layer so that the exchange anisotropy fixes the magnetic moment of the ferromagnetic layer and by changing the magnetic moment of the other ferromagnetic layer in response to an external magnetic field.
As reviewed above, multi-layered thin-film devices made by stacking very thin layers as thin as 100 nm, approximately, have come to be used as magnetoresistance effect elements and other active elements. In these multi-layered thin-film functional devices, characteristics of active elements often vary due to the inter-diffusion of atoms at boundaries between thin-film layers, and thermal stability of their characteristics is an important issue for their practical use.